The present invention relates to a method and apparatus for de-aerating liquids, or separating entrained air or froth from liquids or pulps.
The invention has been developed primarily for use with thickeners, clarifiers, or concentrators and will be described hereinafter with reference to these applications. It will be appreciated, however, that the invention is not limited thereto.
Thickeners, clarifiers and concentrations are typically used for separating solids from liquids and are often found in the mining, mineral processing, food processing, sugar refining, water treatment, sewage treated, and other such industries.
These devices typically comprise a tank in which solids are deposited from suspension or solution and settle toward the bottom as pulp or sludge to be drawn off from below and recovered. A dilute liquor of lower relative density is thereby displaced toward the top of the tank, for removal via an overflow launder. The liquid to be thickened is initially fed through a feedline into a feedwell disposed within the main tank. The purpose of the feedwell is to ensure relatively uniform distribution and to prevent turbulence from the incoming feed liquid from disturbing the settling process taking place within the surrounding tank.
In cases where the feed liquid comprises flotation concentrate, it is normally at least partially aerated. The air bubbles, if allowed to pass from the feedwell into the main tank, tend to produce a considerable amount of relatively stable froth on the surface of both the feedwell and the thickener. This froth can contain a significant proportion of entrained solids and thereby tends to reduce the separation efficiency of the thickener. In addition, air bubbles can become trapped in the sludge, resulting in slower settling rates and lower underflow densities, both of which reduce separation efficiency further still.